Why is the Magnetic lasso tool size not accurate?

[Glenn 8675309]

In working with the magnetic lasso tool,  I come to realize that a magnetic lasso tool size of 100, for example, is not 100 pixels wide, why is that? 

[Greg_S. · Accepted solution]

From the User Manual:

(Optional) Set Magnetic Lasso tool options in the Tool Options bar:

• To specify the area of edge detection, enter a pixel value between 1 and 256 for Width. The tool detects edges only within the specified distance from the pointer.

If you change your cursor, from Precise to Standard (in Preferences), you will see that the size/diameter of the cursor is really of no consequence.  The tool width is measuring (in pixels) how far it should look from the center of the pointer to detect the edge of the object that is being selected.

Does that make sense?

[Glenn 8675309]

Yes it does, The diameter of the "precise" magnetic lasso as depicted in my original post is essentially of no pratical use then, correct?   My personal preference has always been the precise brush with the crosshair... I'll stick with that and just sorta ignore the circle around  it. 

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